Treatment of vinyl alcohol polymer yarns



y 1969 P. J. TERRA ETAL. 3,445,562

TREATMENT OF VINYL ALCOHOL POLYMER YARNS Filed March 25. 1965 I n vemor's 7 ierre 32am 72mm fine/rs e/I91 12 JMMM m )4 771ml) l forneys United States Patent 3,445,562 TREATMENT OF VINYL ALCOHOL POLYMER YARNS Pierre Jean Terra, Lyon, and Andre Pellet, ,Tassin-la- Demi-Lune, France, assignors to Societe Rhodiaceta, Paris, France, a corporation of France Filed Mar. 25, 1965, Ser. No. 442,642 Claims priority, application France, Mar. 25, 1964, 968,673 Int. Cl. B29c 17/02 US. Cl. 264-290 7 Claims ABSTRACT OF THE DISCLOSURE Vinyl alcohol polymer yarns are stretched in a tube which is at an angle between 0 and 25 to the horizontal, whose length, in meters, is between 2/3 and 4/3 the speed of the entry of the yarn into the tube, in meters per minute, which is of small (e.g. 2.5-50 times the diameter of the yarn) and advantageously uniform crosssection throughout its length, which is heated at a temperature between 235 and 250 C., and into and through which, in the direction of the path followed by the yarn, a gaseous fluid at atmospheric pressure and at a temperature between 150 and 250 C. is fed at a rate of flow of 0.5 to 1.7 cubic meters per hour per cm. of crosssection of the tube.

This invention relates to the treatment, in particular the stretching, of yarns of a vinyl alcohol polymer, by means of which it is possible to obtain such yarns having good mechanical properties more readily than by the methods hitherto known.

The term vinyl alcohol polymer is used to denote a long-chain synthetic polymer, at least 50% by weight of which consists of vinyl alcohol units By yarn is meant either a monofilament or an assembly of filaments obtained by wet spinning, dry spinning or semi-melt spinning, including multi-filament yarns and also tows of high count which will subsequently be cut to produce staple fibre.

It is known to stretch yarns of vinyl alcohol polymers in a molten metallic bath at 235 C. The use of such a bath is costly and presents risks of lead poisoning to the operators when it has a lead base, which is generally the case, notably when it consists of Woods alloy or a like mixture. Moreover textile treatments in a molten metal bath result in entrainment of metal particles adhering to the filaments, which are generally difficult to eliminate.

It is also known to stretch yarns of synthetic polymers in a substantially vertical tube, into which a gaseous fluid is injected from the top downwards; this involves certain difficulties, notably a chimney efiect which makes it necessary to fit to the ends of the tube pressure-reducing devices, of the type common-1y known as venturis, in order to facilitate the simultaneous introduction and passage of the yarn and of the fluid in the tube. The problems arising are difficult to solve, especially when the tubes are of large dimensions.

It is also known to stretch yarns of synthetic polymers in a horizontal tube which is so designed that the yarns are subjected therein to the action of a fluid under high pressure.

According to the present invention, vinyl alcohol polymer yarns are stretched in a tube which is at an angle between 0 and 25 to the horizontal, whose length, in metres, is between 2/ 3 and 4/3 the speed of entry of the yarn into the tube, in metres per minute, which is of ice small (e.g. 2.5-50 times the diameter of the yarn) and advantageously uniform cross-section throughout its length, which is heated at a temperature between 235 and 250 C., and into and through which, in the direction of the path followed by the yarn, a gaseous fluid at atmospheric pressure and at a temperature between and 250 C. is fed at a rate of flow of 0.5 to 1.7 cubic metres per hour per cm. of cross-section of the tube.

If the tube is at an angle (not exceeding 25) to the horizontal, it may slope upwards or downwards.

In applying the process of the invention, the speed of introduction of the yarn, and therefore the output of the machine, can be increased simply by increasing the length of the tube. In practice, tubes having a length between 5 and 20 metres are generally the most convenient, having regard to the space requirements, but greater lengths may also be used.

The said tube may be heated, for example by means of a jacket through which a hot fluid is circulated. It is generally advantageous to operate at a temperature in the neighbourhood of 238 C., as giving the best stretch and hence excellent mechanical properties to the yarn.

Although the rate at which the gaseous fluid flows through the tube within the specified range has no substantial effects on the mechanical properties of the yarn or the limit to which it can be stretched, rates above 1.7 cubic metres per hour per square centimetre of crosssection may cause vibrations of the yarn, which may result in breakages. On the other hand, flow rates below 0.5 cubic metre per hour per square centimetre of crosssection do not give good results.

The temperature of the gaseous fluid on entering the tube is preferably between 180 and 220 C. as this usually gives the highest stretching stability and avoids, or reduces to a minimum, sticking of the filaments. Moreover, the use of hot gas makes it unnecessary to dry the yarn before stretching, as is necessary when operating in a molten metal bath. 1

As the gaseous fluid there may be employed any gas or vapour which is inert to the polymer under the operating conditions, for example nitrogen or air. For reasons of economy air will generally be used. The nitrogen or air or other gas or vapour may be charged with any desirable inactive or reactive further substance, and means for recycling it may be provided.

For carrying out the process there may be employed, for example, the apparatus diagrammatically illustrated in the accompanying drawing. In the apparatus a yarn 1 is passed by means of feed rolls 2 into a stretching tube 3, through the inlet of which the gaseous fluid is injected by means of an injector 4. The yarn is drawn from the tube by the stretching rolls 5. The arrows indicate the direction of the travel of the yarn.

If desired, the stretched yarn may be subjected to subsequent shrinkage treatment, for example by heating it in a tube similar to the tube 3, optionally provided with a fluid injector.

The process of the invention can thus be carried out by means of an apparatus of much simpler and less costly construction than the hitherto known devices. It is to be noted that the stretching tube comprises no constriction, either at the inlet or at the outlet, so that it is easy to thread and use. The injected air is readily eliminated and 3 Y e Examples 1 to A vinyl alcohol polymer yarn of 10,500 denier, 200 filaments, is introduced into the tube 3, which is 9 m. long and 14 mm. in diameter, and is heated at 238 C. The injector 4 consists of a tube 6 mm. in diameter, which is narrowed to 2 mm. at the point at which it enters the tube 3. The speed at which the yarn enters the tube 3 is metres per minute, and that at which it leaves is 105 metres per minute, which gives a stretch of 10.5 A number of nms are made, the rate of flow and the temperature of the injected air being varied. The characteristics of the yarn obtained after a subsequent 8% shrinkage are set out in the last two columns of the following table:

By stretch limit is meant the maximum degree of stretch possible without breaking the yarn.

Example 6 A yarn identical to that employed in Examples 1 to 5 is subjected to a stretch of 10.5 X in the same apparatus. Air is injected at a rate of 1.3 cubic metres per hour per square centimetre at a temperature of 180 C. The yarn is then shrunk by 12% in a tube similar to the tube 3.

The yarn obtained has a tenacity of 7.12 g./den., and a dry elongation of 12%.

These properties are at least equal to, and generally rather better than those obtainable by stretching a similar yarn to the same degree in a molten metal bath at 235 C.

Example 7 A yarn identical to that treated in Examples 1 to 5 is stretched under the same conditions as in Example 6 except that the speed of admission of the yarn is 8.75 metres per minute and the degree of stretch is 12X, and is then shrunk by 8%.

The yarn obtained has a tenacity of 8.9 g./den., and a dry elongation of 9%; the stretch limit is 15.5X.

We claim:

1. A process for the treatment of continuous vinyl alcohol polymer yarns, which comprises stretching the yarns in a tubular stretching zone which is at an angle be- "tweii'0' and25 tdthe'horizontal, whose length in metres is between 2/ 3 and 4/3 the speed at which the yarn enters the stretching zone in metres per minute, which is of small cross-section over its entire length, which is heated at a temperature between 235 and 250 C., and into and through which, in the same direction as that in which the yarn travels, a gaseous fiuid at atmospheric pressure and at a temperature between and 250 C. is fed-at a rate of 0.5 to 1.7 cubic metres per hour per square centimetre of cross-section of the stretching zone.

2. A process according to claim 1, wherein the stretching zone is of uniform cross-section throughout its length.

3. A process according to claim 1, wherein the stretching zone is heated to a temperature in the neighbourhood of 238 C. a

4. A process according to claim 1, wherein the gaseous fluid enters the stretching zone at a temperature of 180- 220 C.

5. A process according to claim 1, wherein the gaseous fluid is air.

, 6. A process according to claim 1, wherein the stretched yarn is substantially shrunk.

7. A process for the treatment of continuous vinyl alcohol polymer yarns, which comprises stretching the yarns in a tubular stretching zone which is at an angle between 0 and 25 to the horizontal, whose length in metres is between 2/ 3 and 4/ 3 the speed at which the yarn enters the stretching zone in metres per minute, which is of small and uniform cross-section over its whole length, which is heated to a temperature in the neighbourhood of 238 C., and into and through which, in the same direction as the yarn travels, air at atmospheric pressure and at a temperature of 180-220 C. is fed at a rate of 0.5 to 1.7 cubic metres per hour per square centimetre of cross-section of the stretching zone.

References Cited UNITED STATES PATENTS 2,664,009 12/ 1953 Emerson. 3,048,467 8/ 1962 Roberts et al. 264290 3,170,973 2/1965 Tanabe et al.

FOREIGN PATENTS 531,732 10/1956 Canada.

JULIUS FROME, Primary Examiner.

HERBERT MINTZ, Assistant Examiner.

US. Cl. X.R. 

